Layered Double Hydroxides Materials Research Articles

A Zero-Strain Insertion Cathode Material for Room-Temperature Fluoride-Ion Batteries.

A fluoride-ion battery (FIB) is a novel type of energy storage system that has a higher volumetric energy density and low cost. However, the high working temperature (>150 °C) and unsatisfactory cycling performance of cathode materials are not favorable for their practical application. Herein, fluoride ion-intercalated CoFe layered double hydroxide (LDH) (CoFe-F LDH) was prepared by a facile co-precipitation approach combined with ion-exchange. The CoFe-F LDH shows a reversible capacity of ∼50 mAh g-1 after 100 cycles at room temperature. Although there is still a big gap between FIBs and lithium-ion batteries, the CoFe-F LDH is superior to most cathode materials for FIBs. Another important advantage of CoFe-F LDH FIBs is that they can work at room temperature, which has been rarely achieved in previous reports. The superior performance stems from the unique topochemical transformation property and small volume change (∼0.82%) of LDH in electrochemical cycles. Such a tiny volume change makes LDH a zero-strain cathode material for FIBs. The 2D diffusion pathways and weak interaction between fluoride ions and host layers facilitate the de/intercalation of fluoride ions, accompanied by the chemical state changes of Co2+/Co3+ and Fe2+/Fe3+ couples. First-principles calculations also reveal a low F- diffusion barrier during the cyclic process. These findings expand the application field of LDH materials and propose a novel avenue for the designs of cathode materials toward room-temperature FIBs.

Experimental and Theoretical Studies on the Intercalation of Naproxen into the Mg2Al and Zn2Al Layered Double Hydroxides by Ion Exchange Reaction

In this work, Layered Double Hydroxide (LDH) materials carrying the worldwide administered non-steroidal anti-inflammatory drug naproxen (NAP), and the sodium naproxenate salt (NaNAP) for comparison, were studied by computational approaches aiming to model the structure of hybrid LDH-drug and shed light on NAP intercalation process. Atomic modeling calculations were performed at the quantum mechanical level based on Density Functional Theory and classical force fields based on empirical interatomic potentials. LDHNAP materials were prepared by ion exchange reaction from Mg2Al(OH)6Cl and Zn2Al(OH)6Cl pristine phases. The characterization of the materials confirmed NAP intercalation and also the permanence of the pristine phases in the isolated materials after ion exchange. Crystallographic lattice parameters, elemental analysis, and TGA experimental results were then employed in the calculations, which revealed that NAP anions can completely neutralize the positive charge of the LDH layers: both Mg2Al and Zn2Al LDH structures could be optimized with all Cl− anions substituted by NAP. The drug assumed different dispositions in the NaNAP crystal or when intercalated into LDH. Additionally, infrared wavenumbers calculations agreed with the experimental results and showed useful to support LDHNAP bands assignment. The employed theoretical models to represent the structure of LDHNAP systems are expected to assist the interpretation of future experimental results and to be used as auxiliary tools to tune properties of LDH-drug pharmaceutical formulations.

A Comprehensive Review of Layered Double Hydroxide-Based Carbon Composites as an Environmental Multifunctional Material for Wastewater Treatment

As is well known, hydrotalcite-like compounds, such as layered-double-hydroxide (LDH) materials, have shown great potential applications in many fields owing to their unique characteristics, including a higher anion exchange capacity, a structure memory effect, low costs, and remarkable recyclability. While the lower surface area and leaching of metal ions from LDH composites reduce the process efficiency of the catalyst, combining LDH materials with other materials can improve the surface properties of the composites and enhance the catalytic performance. Among organic compounds, carbon materials can be used as synergistic materials to overcome the defects of LDHs and provide better performance for environmental functional materials, including adsorption materials, electrode materials, photocatalytic materials, and separation materials. Therefore, this article comprehensively reviews recent works on the preparation and application of layered double-hydroxide-based carbon (LDH–C) composites as synergistic materials in the field of environmental remediation. In addition, their corresponding mechanisms are discussed in depth. Finally, some perspectives are proposed for further research directions on exploring efficient and low-cost clay composite materials.

A review on heavy metal ions adsorption from water by layered double hydroxide and its composites

• We selected to review topics related to the specific application of LDH removal of heavy metals. • Classify and summarize its modification methods, absorption properties, composition, structure, and other aspects. • It is determined that future research needs to reduce environmental impact and economic costs to promote the synthesis and use of LDH. • This system summary will provide helpful guidance for preparing high-efficiency LDHs-based adsorbents and offer critical clues to elucidating the adsorption behavior of heavy metals on LDHs-based materials. Heavy metal pollution is highly toxic and persistent, posing a severe threat to human health, agriculture, and the safe environment. Therefore, there is an urgent need for fast and efficient heavy metal removal technology to deal with emergency response to heavy metal leakage. In recent years, the development of a unique layered double hydroxide material has attracted widespread attention in sewage treatment. Due to these fundamental scientific issues, the general concern about environmental pollution management of LDH-based materials, and the recent significant developments in this field, it is necessary to conduct a thematic review. This article summarizes 474 related articles published since 2005 and outlines functionalized layered double hydroxide (LDH) research status as heavy metal adsorption materials. In addition, there is still a lack of reviews on the adsorption characteristics, interaction mechanism, and application of LDHs-based nanomaterials in heavy metal removal. Here, the primary purpose of this article is to systematically summarize LDHs-based materials and their applications in removing heavy metals from aqueous solutions ( Fig. 1 ). First, we will focus on its preparation and modification methods to understand LDH intuitively. Subsequently, the effects of different environmental conditions on factors such as pH, temperature, and contact time were summarized. Finally, the interaction mechanism between LDHs composites and heavy metals is briefly described, and a quick conclusion is given.

Theoretical Study on Photocatalytic CO2 Reduction to CO and CH4 over M(II)2M(III/IV)-Layered Double Hydroxides

Photocatalytic CO2 reduction (CO2PR) is of great significance for high-density solar energy storage and carbon balance, and layered double hydroxides (LDHs) as CO2PR catalysts have attracted much attention. In this work, the electronic properties such as the band structure, density of states and band edge placement of 10 MII2MIII/IV-NO3-LDHs (MII = Mg2+, Co2+, Ni2+, Zn2+; MIII = Al3+, In3+, Cr3+, Fe3+; MIV = Ti4+), thermodynamic mechanism, and thermodynamically favorable products of CO2PR, especially CO and CH4, over these LDHs are investigated by using Hubbard-corrected density functional theory. The calculation results indicate that all LDHs except the Mg2Al- and Mg2In-LDHs are responsive to visible light, and all the LDHs have enough driving force to undergo CO2PR to products except the Ni2Al- and Ni2Fe-LDHs. For Mg- and Zn-containing LDHs, the COOH pathway is favorable, while the Ni2Ti- and Co2Al-LDHs prefer the HCOO pathway. According to the minimum-free-energy reaction pathway, for Co2Fe-LDH, CO2PR prefers to generate HCOOH, and the potential-determining step is HCOO* → HCOOH*. For the Mg2Al-, Mg2In-, Co2Al-, Ni2Ti-, Zn2Al-, Zn2Cr-, and Zn2Ti-NO3-LDHs, CH4 is the favorable final product via HCOOH, HCHO, or CH3OH intermediates. The formation of CO mainly goes through the COOH pathway. The relationship between the effective driving force of CO2PR to CH4 or CO and the adsorption energy of the reactant CO2 or the valence band maximum (VBM) of LDHs reveals that the Mg2In-LDH and Mg2Al-LDH, which have a moderate adsorption and VBM favor CO2PR to CH4 and CO the most, respectively. On the Co2Fe-LDH (110), CO2 prefers to form CH4 than that of the Co2Fe-LDH (003), which indicates that the crystal faces also affect favorable products of CO2PR. This work provides useful information of the photocatalytic performance of LDH materials for CO2PR and is helpful for the design of highly efficient CO2PR catalysts.

Effect of the synthesis pH, the nature of the divalent cations and the metal salt concentration on the formation of layered double hydroxides for removal of Cochineal Red A dye from aqueous solutions

In this research work, removal of Cochineal Red A dye from aqueous solution was studied using layered double hydroxide materials prepared by a coprecipitation method at variable pH. The effects of the synthesis pH, the nature of the divalent cations and the total metal salt concentration on the formation of layered double hydroxides and their application to the removal of Cochineal Red A dye from aqueous solution were investigated. The structure of the materials prepared was characterized by X-ray diffraction and Fourier transform infrared. It was found that the nature and content of the bi- and trivalent metal ions in the layered double hydroxide influenced the adsorption. Ni–Fe had 0.96 to 1.70 times more adsorption capacity before reaching its equilibrium adsorption than Zn–Fe prepared at pH 7–9 with 2.2 M of total metal salt concentration. No difference was observed in the amount of Cochineal Red A dye adsorbed onto Zn–Fe prepared at both pH 7–9 and pH 10–11 in the range 1.1–3.3 M of total metal salt concentration. The results show that the increase in the precipitation pH leads to decreasing adsorption capacity. The Cochineal Red A dye adsorption follows the Temkin model for the Ni–Fe and Zn–Fe prepared at pH 7–9 and follows the Langmuir model for the Zn–Fe synthesized at pH 10–11 with high coefficient correlation. The adsorption kinetics data fitted the pseudo-second-order model. A thermodynamic study indicates that the adsorption process is both spontaneous and endothermic in nature.

Synthesis and characterisation of layered double hydroxides with varying divalent metal cations: Mg2+, Zn2+, Ca2+

This study aims to investigate the physicochemical properties of layered double hydroxides (LDH) with different divalent metal (M2+) cations. A series of nitrate-based LDH materials was synthesised by using aluminium (Al3+) as a trivalent cation (M3+) with varying M2+ cations such as magnesium (Mg2+), zinc (Zn2+), and calcium (Ca2+) ions to prepare magnesium–aluminium-layered double hydroxide (MgAl-LDH), zinc–aluminium-layered double hydroxide (ZnAl-LDH), and calcium–aluminium-layered double hydroxide (CaAl-LDH), respectively. MgAl-LDH and ZnAl-LDH were synthesised by the co-precipitation method, whereas CaAl-LDH was prepared by the hydrothermal method. The samples were characterised by powder X-ray diffraction (PXRD), Fourier transform infrared spectra (FTIR), thermogravimetric and differential thermogravimetric analysis (TGA/DTG), field emission scanning electron microscope (FESEM), and accelerated surface area and porosity (ASAP) analysis. The PXRD patterns show that MgAl-LDH (9.8 Å) had the greatest interlayer spacing, followed by ZnAl-LDH (8.9 Å), and CaAl-LDH (8.7 Å). The FTIR spectra clearly confirms the presence of nitrate ions in the LDH structure. Two-step degradation behaviour of the samples was observed in the TGA curve. The LDHs exhibit Type IV isotherms and hexagonal structures were observed on the FESEM images.

Innovative membrane containing iron-based layered double hydroxide intercalated with phyto therapeutic diterpenoid

This work developed an innovative membrane based on the high-performance PEBAX®2533 (PEBA) block copolymer and particles of iron-based layered double hydroxide (LDH) (Mg4FeAl layer composition) intercalated with phytotherapeutic abietate anions (ABI); both guest and host species are active in the promotion of wound healing. The presence of conjugated double bonds in the ABI structure promotes chemical reactions confronting its stability. Hence, LDH can protect the phytochemical species and promote its modified release. Aiming the development of wound dressings, LDH-ABI particles were immobilized in a biocompatible polymer (PEBA) by simple casting method. All samples were characterized by X-ray diffraction (XRD), vibrational (infrared and Raman) spectroscopies, thermogravimetry analysis coupled to mass spectrometry (TGA-MS), elemental chemical analyses and, in the case of polymer composites, by mechanical tests. Although the intercalation of organic anions into iron-based LDH materials is challenging, ABI intercalation was successful and using one-pot method (coprecipitation at constant pH value), according to XRD data. Additionally, spectroscopic techniques indicated the integrity of the ABI chemical structure after intercalation. The sodium abietate (NaABI) salt and the PEBA_NaABI membrane were also prepared to evaluate the effect of LDH in the formulations. In vitro release assays in saline solution at 32 °C showed the release (or solubilization) of around 3 and 5 wt./wt% of the ABI amount from LDH and salt, respectively, after 10 h. Comparatively, ABI release from the PEBA_Mg4FeAl-ABI and PEBA_NaABI formulations was improved to 20 and 22 wt%, respectively. The improvement in ABI release profiles from the membranes was related to the decrease in particles aggregation and improved media permeation. LDH particles released bioactive Mg2+ cations in the saline solution and, unlike NaABI particles, also improved the mechanical performance of the polymer. Thus, PEBA_Mg4FeAl-ABI showed promising as a component of wound dressings.

Facile synthesis of Ni-based layered double hydroxides with superior photocatalytic performance for tetracycline antibiotic degradation

The purpose of this study was to investigate the photocatalytic performance of Ni-based layered double hydroxides (LDHs) in degradation of tetracycline (TC) as a model antibiotic pollutant. Two kinds of Ni-based LDHs (NiFe-LDH and NiCr-LDH) with chloride and carbonate ions in the interlayer region were facile fabricated by chemical co-precipitation method at room temperature and characterized using Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy disperse spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) techniques. The results showed that the as-prepared LDHs materials performed superior photocatalytic efficiency to eliminate TC from aqueous water solution under UV–vis light irradiation. The photocatalytic efficiency depends on the catalyst dosage and TC concentration. Furthermore, the plausible photocatalytic degradation mechanism was proposed by means of radical trapping and electron spin resonance (ESR) tests. It is found that the photocatalytic degradation of TC by Ni-based LDHs follows an oxygen-induced pathway, and the superoxide radical (•O2−) and hydroxyl radical (•OH) play a major role in the photocatalytic degradation process. The study provided a valuable insight into fabricating high-performance and environmentally friendly LDHs for removal of antibiotics in waste water.

Preparation of well-structured hybrid material through ion exchange of chloride by 2,4,5-trichlorophenoxyacetic herbicide in a layered double hydroxide

The [Zn2–Al–Cl] layered double hydroxide (LDH) was used to successfully exchange chloride ions by 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), as a model of the carboxylate herbicide family. The total exchange was obtained after 6 h of stirring with a 2,4,5-T/Cl molar ratio of 10 and a pH of 7. The characterization by various techniques (XRD, FTIR, TG-DTG and SEM) indicates that this exchange led to the production of a new stable hybrid LDH phase intercalated by the herbicide. The structural analysis of the material, based on the interlayer distance of 1.855 nm, indicates that the 2,4,5-T anion takes a vertical arrangement in a double layer. The cohesion of the structure is ensured by hydrogen bonds between the carboxylate group of the herbicide and the hydroxyl groups of the LDH sheets. The exchange causes a modification of the type of symmetry from a 3R stacking mode for [Zn2–Al–Cl] (space group R3‾m) to a 2H for [Zn2–Al-2,4,5-T] (space group P63/mmc). This result confirms the already proven use of LDH materials as efficient anion exchangers for the trapping and elimination of this type of pollutant from wastewater.

Effect of intercalation of flocculant on adsorption properties of ZnMgAl-LDHs

Layered double hydroxides (LDHs) have emerged as promising dyestuff sorbents due to their interlayer pluggability and high anion exchange capacity. Three kinds of flocculants (anionic, cationic and nonionic polyacrylamide) doped ZnMgAl LDHs were prepared by co-precipitation method. The influence of different polyacrylamide types and different amounts of polyacrylamide on the adsorption properties were evaluated. The results showed that the adsorptive capacity of methyl orange (MO) by LDH-c2 (prepared by co-precipitation method and the ratio of cationic intercalation with aluminum mass was 1:100) was 1251 mg/g. Flocculant intercalation might be an effective way to improve the adsorption performance of LDHs materials.

Layered Double Hydroxide Nanomaterial as Highly Efficient Adsorbent and its Recycling after Removal of a Carcinogenic Tartrazine Dye from Wastewater

In this work, the tartrazine dye is removed from the wastewater by the layered double hydroxide (LDH) [Zn2-Al-Cl]. LDH materials have proven to be highly effective in removing pollutants, with a low cost of synthesis, non-toxic, and they do not regenerate the sludge. Several parameters were studied, the retention of dye by LDH nanomaterial is optimized for a pH between 6 and 8, the equilibrium retention is obtained after 24 hours, and retention kinetics follows the pseudo-second-order model. The isotherms are the H type, and they follow the Langmuir model, retention capacity reaches 100% for a mass ratio (adsorbate/adsorbent) between 0.1 and 0.5, and the maximum amount retained of the dye is 740.35 mg/g for an initial concentration of tartrazine was 1200 mg/L and 100 mg of mass of LDH. X-ray diffraction (XRD) showed that the synthesized matrix is crystallized in a lamellar structure. Two processes affect the removal of the dye, adsorption of the surface of LDH, and intercalation between the layers. Infrared analysis indicated the appearance of the band's dye in the spectrum of the matrix after retention. Moreover, scanning electron microscopy showed the lamellar character of the two phases obtained before and after retention. The thermodynamics study showed that the process is endothermic, and the adsorption mechanism is governed by physisorption. The LDH nanomaterial is a good adsorbent with low cost, high efficiency, and recyclable.

Tailoring the properties of polyamide thin film membrane with layered double hydroxide nanoclay for enhancement in water separation

This current paper presented a new candidate and potentially to improve the current membrane materials in water filtration process. With that, the primary materials used in this research study is layered double hydroxides (LDH) nanoclay which can be obtained from earth minerals and self-synthesized from inorganic salts were discussed thoroughly to help a better understanding of these materials. However, the current technologies of water separation were still lagging behind and ineffective especially in removal of divalent metal ions and multivalent salts. Infeasibility of reverse osmosis membrane make it not a viable option for divalent salts filtration. With that, nanofiltration (NF) membrane offered as an alternative to substitute available method. In this study, thin film nanocomposite (TFN) membranes were fabricated by incorporating layered double hydroxides (LDH) nanoclay. The LDH nanoclay with different loading ratio of 0, 0.05, 0.1, 0.15 and 0.2 were impregnated into polyamide layer on top of polysulfone substrates. The fabricated TFN were characterized in terms of physicochemical properties (SEM and FTIR) and membrane hydrophilicity (contact angle). After the addition of LDH, the morphological structures of TFN membranes were changed and the surface hydrophilicity was enhanced significantly. FESEM images displayed a typical ridge and valley morphology with nodule-like structures. As the LDH loading was increased, the contact angle decreased from 34.56° to 15.76° showing the surface hydrophilicity of membrane is improved. The separation performance of membrane was evaluated in terms of salt rejection ability by cross flow filtration system. The best performance NF membrane was found to be TFN 0.05 with high water flux and MgCl2 rejection with values of 24.18 L/m2.h and 91% respectively. This study has experimentally validated the potential of LDH materials in membrane process for improvement in water separation process.

Preparation, characterization and antibacterial applications of ZnAl- LDH with the diaminododecylphosphonic acid intercalation

Layered double hydroxides (LDHs) have been widely investigated in a wide range of applications in health, in the pharmaceutical industry and in the material of biotechnology industries. This material can be considered as a group of promising materials in the development of new health applications. The combination of phosphonic acid with LDHs material create a new hybrid material with new properties.In this work the synthesis of Zn/Al double lay-ered hydroxides by chemical co-precipitation method (molar ration 2) and grafted with Diamino Dodecyl Phosphonic Acid (DDPA) via anion-exchange mechanism. The samples were characterized and confirmed by X-ray diffraction (XRD), and the presence of diamino dodecyl phosphonic acid (DDPA ) was verified by Elemental analysis, BET analysis, and infrared spec-troscopy. Both of the samples were found to be showing antibacterial activ-ity. The zone diameters of Zn-Al- LDH were 40 mm and 25 mm for Esche-richia coli(ATCC 25922) and Streptococcus (ATCC 25922)and 20 mm for bacillus (ATCC 25922) whereas the same for hybrid LDH (Zn-Al-DDPA)were43 mm , 32 mm and 25 mm for the same bacteria showing stronger antibacterial activity of the grafted material over the material itself. The experimental results confirm the application of Zn-Al-DDPA in the field of antibacterial activities and may offer a promising antibacterial elucidation to the society.

Facile construction of cellulose/layered double hydroxides nanocomposite membranes with high strength and antibacterial properties

AbstractHigh‐strength regenerated cellulose/ZnAl‐layered double hydroxides (LDH) composite membranes (RCL) with good mechanical and antibacterial performance were developed by stirring vigorously cellulose and LDH in NaOH/urea aqueous solvent system at −12°C. The obtained cellulose/LDH composited materials were characterized and the results indicated that well dispersion of LDH in the cellulose matrix. The tensile strength of RCL membranes were enhanced to 92.1 MPa from 68.3 MPa for that of RC film because of the strong interfacial interaction between the LDHs and cellulose matrix as well as the high rigidity of the LDHs. The addition of LDH into the cellulose could improve the thermal stability, water resistance, and flame retardant of the regenerated cellulose film. Zn2+ ions were exited in the cellulose/ZnAl‐LDH materials, leading to good antibacterial activities against Staphylococcus aureus and Escherichia coli, which is important for RCL composite materials in antibacterial packaging filed.

Active Corrosion Protection of Mg–Al Layered Double Hydroxide for Magnesium Alloys: A Short Review

Layered double hydroxides (LDHs) have been successfully applied in surface protection and functionalization of metal materials owing to their special structure, composition, controllability, anion exchange, and other excellent properties. Herein, this review focused on the most common LDH preparation methods on magnesium alloys in the past 10 years by summarizing about 70 research papers. At the same time, based on the corrosion protection mechanism of LDH materials, the performance of LDH films and LDH as filler on metal substrates was briefly introduced. The surface of LDH materials were chemically modified to enhance their compatibility with solvents, and their corrosion resistance function was developed as an additive. Finally, LDH-based composite coatings on Mg alloys by surface pretreatment and chemical modification were discussed.

Ciprofloxacin in Layered Double Hydroxides: Looking for the Best Synthesis Method

It is important to develop new methods of release to improve pharmacokinetic parameters of drugs, especially antibiotics, whose plasmatic concentration is determinant to ensure an effective treatment. Layered double hydroxides (LDH) are inorganic and biocompatible materials with high drug intercalation capacity and release properties that can be tuned by controlling the pH value. These materials can be an excellent choice to achieve a sustained release and an optimal drug concentration in plasm. In this work, LDH were synthesized with intercalated ciprofloxacin (CIP) by three different methods: coprecipitation, reconstruction and ion exchange. LDH-CIP complexes were characterized by XRD, TG-DSC, TEM, SEM, FTIR, electrophoretic mobilities, and drug release and dissolution kinetics in NaCl solutions and under physiological conditions. The coprecipitation and reconstruction methods lead to the formation of ill-defined products, whereas the ion exchange method rendered the best intercalation results. CIP release was controlled by dissolution at pH<3 and by desorption and ion exchange at intermediate and high pH. In comparison with a commercial formulation, the LDH-CIP complex prepared by ion exchange presented a slower release profile. The fast dissolution at gastric pH raises the need of developing some type of coating for protecting LDH materials.

The catalytic mechanism of intercalated chlorine anions as active basic sites in MgAl-layered double hydroxide for carbonyl sulfide hydrolysis.

In order to make clear the role of intercalated anions in layered double hydroxides (LDHs) for catalytic hydrolysis of carbonyl sulfide (COS), the adsorption and reaction characteristics of COS over the simple Mg2Al-Cl-LDH model catalyst were studied by both theoretical and experimental methods. Density functional theory (DFT) calculations by CASTEP found that the chloride ions in LDH function as the key Brønsted base sites to activate the adsorbed H2O with enlarged bond length and angle, facilitate the dissociative adsorption of intermediates including mono-thiocarbonic acid (MTA) and hydrogen thiocarbonic acid (HTA), and participate in the formation of transient states and subsequent hydrogen transfer process with decreased energy barriers during COS hydrolysis. COS hydrolysis will preferentially go through the dissociated intermediates of mono-thiocarbonates (MT) and hydrogen thiocarbonates (HT) with dramatically decreased energy barriers, and the rate-determining step of COS hydrolysis over Mg2Al-Cl-LDH will be the nucleophilic addition of C=O in COS by H2O (Ea = 1.10 eV). The experimental results further revealed that the apparent activation energy (0.89 eV) of COS hydrolysis over Mg2Al-Cl-LDH is close to theoretical value (1.10 eV), and the accumulated intermediates of MT, HT, or carbonate were also observed by FT-IR around 1363 cm-1 on the used Mg2Al-Cl-LDH, which are well in accordance with the theoretical prediction. The demonstrated participation of intercalated chlorine anions in the evolution of intermediates and transient states as Brønsted base sites during COS hydrolysis will give new insight into the basic sites in LDH materials.

Recent progress and challenges in photocatalytic water splitting using layered double hydroxides (LDH) based nanocomposites

The worldwide energy demand is steadily increasing and estimated to be doubled by the year 2050 due to a continuous hike in economies and population. A large part of the global energy requirement procures using traditional energy sources such as fossil fuels, which are non-renewable. Also, their excessive consumption imparts negative impacts on the environment by CO2, and CO emissions, which constantly increase the average global temperature. Therefore, the need for a more reliable, sustainable, inexpensive, renewable and environmentally-friendly form of energy is imperative. From these perspectives, hydrogen energy is emerging as one of the most promising alternatives to overcome rising energy demand with a zero-carbon footprint.Herein, various layered double hydroxides (LDH) nanocomposite owing to their attractive physicochemical properties and synergistic effect with other materials in the field of hydrogen production are reviewed. Why the class of LDHs materials is critical and their ideographic properties which make them promising materials in the field of water splitting via photocatalysis and electrocatalysis are also discussed. The synthetic methods of LDHs based nanocomposites fabrication are summarized. Various challenges and strategies from the viewpoint of a different method of hydrogen production through LDHs are reported. Additionally, multiple techniques like surface plasmon resonance (SPR), heterojunction formation, and doping with co-catalyst to increase the efficiency for photocatalytic hydrogen production are also presented. Hopefully, this review will help the readers explore highly efficient, inexpensive and stable LDH catalysts toward photocatalytic water splitting.

Tuning Dynamically Formed Active Phases and Catalytic Mechanisms of In Situ Electrochemically Activated Layered Double Hydroxide for Oxygen Evolution Reaction.

The active phase and catalytic mechanisms of Ni-based layered double hydroxide (LDH) materials for oxygen evolution reaction (OER) have no common consensus and remain controversial. Moreover, engineering the site activity and the number of active sites of LDHs is an efficient approach to advance the OER activity, as the thickness and stacking structure of the LDHs layer limit the catalytic activity. This work presents an interesting in situ approach of tuning the site activity and number of active sites of NiMn-LDHs, which exhibit the superior OER performance (onset overpotential of 0.17 V and overpotential of 0.24 V at 10 mA cm-2). The fundamental mechanistic insights and active phases during the OER process are characterized by in operando techniques along with the computational density functional theory calculations, revealing that the Ni site constitutes the OER activity and the dynamically generated NiOOH moiety is the active phase. We also prove that Ni sites undergo a reversible oxidation state under the working conditions to create active NiOOH species which catalyze the water to generate oxygen. These findings suggest that the Ni(III) phase in NiMn-LDHs is the OER active site and Mn promotes the electronic properties of Ni sites. Utilizing in situ/in operando techniques and theoretical calculation, we find that the in situ intercalation of guest anions allows the expansion of the LDH layers and keeps the active NiOOH species under the oxidation state of +3 via electron coupling, which ultimately tunes the site populations and site activity toward the superior OER activity, respectively. This work thus targets to provide insight into strategies to design the next generation of highly active catalysts for water electrolysis and fuel cell technologies.